It is becoming increasingly apparent that many of the intracellular physiological activities in mammalian cells that involve Ca.sup.2+ as a second messenger are mediated by calmodulin (CAM). This ubiquitous Ca.sup.2+ -binding protein has an ability to activate a variety of enzymes in a Ca.sup.2+ -dependent manner. Among these enzymes is Ca.sup.2+ and calmodulin-dependent cyclic-nucleotide phosphodiesterase (CaM-PDE) and calmodulin-sensitive Kinase II (CaM-kinase II).
A variety of substances inhibit the activation properties of calmodulin on the calmodulin-dependent enzymes. It has been shown that drugs that inhibit calmodulin sensitive processes are also potent inhibitors of the growth and viability of tumor cells (Hait et al., . "Characterization of the Cytotoxic Effects of Calmodulin Inhibitors" Biochem Pharmacol. 34:3973-3978 (1985); Hait et al. "Calmodulin: A Potential Target for Cancer Chemotherapeutic Agents" J. Clin. Oncol. 4, 994-1012 (1986)). Thus, substances that inhibit calmodulin-mediated enzyme activites may affect cell viability, and possibly other cellular phenomena, through their interactions with calmodulin.
Recently, two new inhibitors of CaM-PDE were discovered (Nakanishi et al., "KS-501 and KS-502, New Inhibitors of Ca.sup.2+ and Calmodulin-Dependent Cyclic-Nucleotide Phosphodiesterase from Sporothrix sp" J. Antibiotics 42:1049-1055 (1989)). These inhibitors of CaM-PDE are naturally occurring metabolites of the organism Sporothrix sp. KAC-1985 and have been designated KS-501 and KS-502 by their discoverers. The chemical structures of these inhibitory compounds are shown below: ##STR1##
The KS-501 and KS-502 compounds inhibit CaM-dependent activities of CaM-PDE in the 1-5.mu.M concentration range. Much higher concentrations of these compounds are required to inhibit CaM-independent activities of these enzymes. Furthermore, these compounds had no effect on protein kinase C which is another Ca.sup.2+ -dependent enzyme but which does not require calmodulin for its activity. Thus, the inhibitory properties of these compounds resides in their interactions with calmodulin.
These inhibitors of CaM-PDE, KS-501 and KS-502, are structurally similar to the naturally occurring compounds known as "TPI compounds" (Yaginuma et al., FR 2,579,599, 03 October 1986), differing only in the sugar content of the molecules. The "TPI compounds" are isolates of the organism Nodulisporium sp. M5220 which also display some inhibitory activity against phosphodiesterases. Currently, it is not known whether the "TPI compounds" inhibit the Ca.sup.2+ and CaM-dependent enzymes.
To date, these inhibitory compounds, including KS-501 and KS-502, have been isolated as metabolic byproducts of microorganisms. Since these microorganisms require facilities for their growth and maintenance, there is a need to produce these specific substances by organic synthetic routes in order to ensure an unlimited supply of these compounds. Even more importantly, such organic synthetic routes will enable the production of other compounds that possess the sought enzyme inhibitory activities, particularly the CaM-mediated enzyme inhibitory activities. These other compounds with CaM-mediated enzyme inhibitory activities will expand the available repertoire of such substances.